The corrosion, transport and deposition of copper and copper-based metals in steam generating systems has been the subject of increasing concern in the industrial boiler marketplace. The copper corrosion in these systems is primarily caused by the presence of dissolved oxygen, carbon dioxide, ammonia and uncontrolled pH. Copper oxides are released as particulate oxides, soluble Cu(I)/Cu(II) and metallic copper species. Copper oxides are relatively unstable and can dissolve, break-up and continually re-deposit within a boiler system.
The consequences of such copper corrosion are the loss of metal potentially leading to failure or requiring expensive maintenance, transport of copper corrosion products to the boiler surfaces, leading to decreased heat transfer and loss of productivity, and depositing of copper metal on less noble metal surfaces causing galvanic corrosion. Copper discharge is also a health and environmental concern due to its toxicity.
Accordingly, it is common practice to introduce corrosion inhibitors into the boiler system. These materials interact with the metal to directly produce a film which is resistant to corrosion, or to indirectly promote formation of protective films by activating the metal surface so as to form stable oxides or other insoluble salts. However, unlike ferrous metals which form insoluble, protective oxides, copper alloys form oxides that are non-protective, allowing further corrosion of the underlying metal to continue.